1. Field of Invention
The present invention relates to a process for production of L-aspartic acid from maleic acid and ammonia characterized by recycling a reaction solution to prevent the discharge of waste water containing a large amount of ammonia, and to L-aspartic acid crystals accompanied with maleic acid and/or salt thereof.
2. Related Art
Various processes for production of L-aspartic acid from ammonium fumarate using microorganisms having aspartase activity are known. For example, there are a process wherein a microorganism resistant against .alpha.-aminobutylic acid is cultured and the cultured cells are used for the reaction (Japanese Examined Patent Publication No. 61-29718), a process using microbial cells cultured in a fumaric acid-containing medium (Japanese Laid-Open Patent Publication No. 60-120983), a process using a column filled with Escherichia coli immobilized in natural polysaccharides (Japanese Laid-Open Patent Publication No. 53-6483), or the like.
Various advanced processes using aspartase or microorganisms having aspartase activity have been developed, but fumaric acid which is more expensive than maleic acid is used as the substrate, so that the costs of raw materials are still high.
The L-aspartic acid is usually recovered by precipitation of L-aspartic acid crystals by addition of a mineral acid such as sulfuric acid to the reaction solution, and separation of the crystals. In this case, a large amount of byproduct such as ammonium sulfate is generated. Thus, for economical and environmental reasons, a process -wherein L-aspartic acid is precipitated and the mother liquors are recycled in a closed system is very desirable.
U.S. Pat. No. 4560653 discloses a process for production of L-aspartic acid wherein aspartase or aspartase-producing microorganism is reacted with fumaric acid and ammonia, and L-aspartic acid is precipitated by addition of maleic acid and filtrated from the solution and the mother liquors are recycled. However, to convert maleic acid in the mother liquors to fumaric acid, the reaction solution is heated with a chemical catalyst such as bromide. Accordingly this is obviously a troublesome process containing removal of the chemical catalyst and the trace color bodies prior to recycle of mother liquors.